linux-kernel - Re: [PATCH] Btrfs: prevent deletion of mounted subvolumes

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Date:	Wed, 1 Apr 2015 13:22:42 +0200
From:	David Sterba <dsterba@...e.cz>
To:	Omar Sandoval <osandov@...ndov.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	Timo Kokkonen <timo.kokkonen@...code.fi>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] Btrfs: prevent deletion of mounted subvolumes

On Wed, Apr 01, 2015 at 12:03:28AM -0700, Omar Sandoval wrote:
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1024,6 +1024,10 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
>  	struct btrfs_root *root = info->tree_root;
>  	char *compress_type;
>  
> +	if (dentry != dentry->d_sb->s_root) {
> +		seq_puts(seq, ",subvol=");
> +		seq_dentry(seq, dentry, " \t\n\\");

Unfortunatelly this does not work if the default subvolume is not the
toplevel one and the implicit mount (ie. without subvol=) is used. Then
this leads to subvol=/ although it should be subvol=/the/default .

There was a patch to build the path in the show_options callback, but it
looked too heavy (taking locks, doing lookups). This is unrelated to the
problem reported by Timo, though the fix might also fix this one.
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